The invention relates to a process for preparing an ethylene amine mixture by hydrogenation of an amino nitrile mixture over a catalyst. The individual ethylene amines can, if appropriate, be isolated from the resulting ethylene amine mixture.
It is generally known that nitriles can be hydrogenated to the corresponding amines in the presence of catalysts. The known processes give the desired products, for example primary amines as main product and secondary and tertiary amines as by-products, as a function of the reaction parameters selected.
It is also known, in processes for preparing amines by hydrogenation of nitrites, that a certain amount of ammonia improves the selectivity of the hydrogenation to primary amines and suppresses the formation of secondary and tertiary amines. However, the hydrogenation in the presence of ammonia results in an additional engineering outlay associated with the separation from the product stream, the work-up and the possible recirculation of the ammonia. Furthermore, relatively high pressures can be necessary in the hydrogenation, since the partial pressure of ammonia has to be taken into account.
Thus, ethylenediamine (EDA), which is a starting material for, for example, the synthesis of complexing agents or bleaching activators which are used, inter alia, as detergent additives or additives to cleaners, can be produced as main product by hydrogenation of aminoacetonitrile (AAN). In an analogous way, the hydrogenation of iminodiacetonitrile (IDAN) gives diethylenetriamine (DETA) as main product. However, DETA or EDA are always formed as by-products in the hydrogenation of AAN or IDAN, respectively.
Numerous processes for the hydrogenation of the α-amino nitriles aminoacetonitrile (AAN) and iminodiacetonitrile (IDAN) or of β-amino nitrites are described in the prior art. It is known that the hydrogenation of β-amino nitrites generally proceeds without problems, while the hydrogenation of α-amino nitrites is associated with the occurrence of numerous disadvantages such as hydrogenolysis of the C—CN bond or the R2N—C bond. “Handbook of Heterogeneous Catalytic Hydrogenation for Organic Synthesis, pp. 213-215” illustrates the problems encountered in the hydrogenation of α-amino nitriles for the example of α-alkylamino nitriles or cyclic α-amino nitrites compared to β-amino nitriles. The known stability problems of α-amino nitriles are presumably the main reason why up to the present day only the hydrogenation of the α-amino nitriles AAN and IDAN to EDA (ethylenediamine) and DETA (diethylenetriamine), respectively, has been described in detail. However, EDA and DETA are prepared industrially by the EDC and MEA processes described below. In the case of higher α-amino nitriles, however, a corresponding hydrogenation is not known.
DE-A 3 003 729 describes a process for the hydrogenation of aliphatic nitriles, alkyleneoxy nitriles and alkyleneamino nitriles to primary amines over a cobalt or ruthenium catalyst in the presence of a solvent system. The solvent system used comprises water and ammonia together with an ether or polyether. The alkyleneamino nitriles or alkyleneoxy nitriles which can be used as starting materials are in each case defined by means of complex general formulae. As specific compounds or examples which can be hydrogenated to the corresponding diamine, mention is made of, inter alia, ethylenediaminedipropionitrile (EDDPN; also referred to as N,N′-bis(cyanoethyl)ethylenediamine) or 3,3′-(ethylenedioxy)dipropionitrile. On the other hand, DE-A 3 003 729 discloses no pointer to the use of individual compounds such as AAN or EDA derivatives having cyanomethyl substituents, e.g. ethylenediaminediacetonitrile (EDDN) or ethylenediaminemonoacetonitrile (EDMN). In addition, the tatter does not come under the general definition of alkyleneamino nitriles according to this document.
EP-A 0 382 508 describes a process for the batchwise preparation of acyclic, aliphatic polyamines by hydrogenation of acyclic, aliphatic polynitriles in the liquid phase over Raney cobalt catalysts, preferably in the presence of anhydrous ammonia. Here, a polynitrile solution is fed into a reaction zone which comprises the Raney cobalt catalyst in an essentially oxygen-free atmosphere. During the entire reaction time, the polynitrile solution is fed in at a rate which is no greater than the maximum rate at which the polynitrile reacts with the hydrogen in the reaction zone. Further mention is made of a reaction parameter K which is suitable for determining the volume feed rate. The process described is restricted to the preparation of polyamines from polynitriles such as iminodiacetonitrile (IDAN), nitrilotriacetonitrile (NTAN) or further compounds having 2 or more cyano groups. However, the reaction of compounds having one cyano group, e.g. AAN to form EDA, is not described.
EP-A 212 986 relates to a further process in which aliphatic polynitriles can be hydrogenated in the presence of a liquid primary or secondary amine comprised in the feed stream over a granular Raney cobalt catalyst to form the corresponding polyamines. Mention is made of, inter alia, the amino component EDA which has to be present and also numerous further primary or secondary amines. This document also specifically states that IDAN can be hydrogenated to DETA.
DE-A 1 154 121 relates to a process for preparing ethylenediamine, in which the starting materials hydrocyanic acid, formaldehyde, ammonia and hydrogen are reacted in the presence of a catalyst in a one-pot process. Both the ammonia and the hydrogen are used in a molar excess over the further reactants hydrocyanic acid and formaldehyde which are present in equimolar amounts. In this process, the AAN formed in situ is therefore not isolated but is directly reacted further with hydrogen. A disadvantage of this process is that the desired product (EDA) is obtained relatively unselectively in small amounts.
U.S. Pat. No. 3,255,248 describes a process for the hydrogenation of organic nitrogen-carbon compounds which preferably have nitro, N-nitroso, isonitroso, cyano or aromatic-substituted amino groups to the corresponding amines in the liquid phase using a sintered catalyst comprising cobalt or nickel. Here, the starting material is sprinkled down either alone or in the presence of a solvent, for example water, tetrahydrofuran, methanol, ammonia or the reaction product formed, together with the hydrogen onto the catalyst. If compounds which are unsaturated on the nitrogen atom, e.g. cyano groups, are hydrogenated, the presence of ammonia in the reaction is recommended. This is made clear in example 1 of this patent where aminoacetonitrile is sprinkled down in the from of an aqueous solution together with liquid ammonia but without another solvent onto the sintered catalyst.
EP-A 1 209 146 relates to a further process for the continuous hydrogenation of nitriles to primary amines, in which the respective nitriles are hydrogenated in the liquid phase over a suspended, activated Raney catalyst based on an alloy of aluminum and the reaction is carried out in the absence of ammonia and basic alkali metal or alkaline earth metal compounds. Nitriles which can be converted into the corresponding ethylene amines are, among many others, AAN, IDAN, EDTN, EDDPN or ethylenediaminemonopropionitrile (EDMPN).
EP-B 0 913 388 relates to a process for the catalytic hydrogenation of nitriles, which comprises contacting of the nitrile with hydrogen in the presence of a cobalt sponge catalyst under conditions for carrying out the conversion of the nitrite group into the primary amine. The cobalt sponge catalyst has been treated beforehand with a catalytic amount of lithium hydroxide and the process is carried out in the presence of water. Suitable nitrites are aliphatic nitriles having from 1 to 30 carbon atoms, including β-amino nitriles such as dimethylaminopropionitrile. A further process for preparing polyamines from the corresponding polynitriles is disclosed in DE-A 27 55 687. In this process, the hydrogenation is carried out over a hydrogenation catalyst in pellet form in the presence of a stabilizer which inhibits decomposition of the catalyst. As polynitrile, it is possible to use, inter alia, ethylenediaminedipropionitrile (EDDPN). A suitable stabilizer is, inter alia, EDA.
US-A 2006/0041170 relates to a process for preparing TETA, in particular TETA salts, and their use as drugs. In this multistage process, EDDN is prepared first. EDDN is subsequently reacted with benzaldehyde to form a (cyclic) imidazolidine derivative. This cyclic compound, which has two cyano groups, is reduced, for example by reaction with hydrogen, to give the corresponding cyclic diamino compound. This diamino compound is in turn hydrolyzed in the presence of an acid to give the corresponding TETA salt. In an alternative embodiment, the cyclic diamino compound is likewise reacted with benzaldehyde to form the corresponding diimino compound which is subsequently again hydrolyzed in the presence of an acid to give the corresponding TETA salt. A further process alternative described in this document is reaction of EDDN with Boc protective groups (tert-butoxycarbonyl groups). The EDDN derivative protected by two Boc protective groups obtained in this way is subsequently hydrogenated to give the corresponding protected TETA derivative. The Boo protective groups are removed by acid hydrolysis to give the corresponding TETA salt. A disadvantage of this process described in US-A 2006/0041170 is, in particular, that it is a multistage hydrogenation process in which the starting material EDDN used firstly has to be chemically converted into a derivative in order to carry out the hydrogenation. A further disadvantage is that TETA is initially obtained as salt and not in the free base form.
The preparation of higher ethylene amines such as triethylenetetramine (TETA) or tetraethylenepentamine (TEPA) by direct hydrogenation of the corresponding α-amino nitriles has not yet been described. Higher ethylene amines such as TETA or TEPA are prepared (industrially) by other processes.
EP-A 222 934 relates to a process for preparing higher alkylene polyamines by reaction of a vicinal dihaloalkane with an excess of ammonia in the aqueous phase with addition of a strong base, resulting in formation of an imine intermediate which is subsequently reacted with an alkylene polyamine to form the higher alkylene polyamine. A suitable vicinal dihaloalkane is, in particular, ethylene dichloride (EDC or 1,2-dichloroethane). Alkylene polyamines used are, in particular, ethylenediamine or higher ethylene amines such as DETA and also TETA and TEPA. In these processes (EDC processes), a mixture of various ethylene amines (linear ethylene amines such as EDA, DETA, TETA, TEPA or higher ethylene amines and cyclic derivatives such as piperazine (Pip) or aminoethylpiperazine (AEPip)) is obtained. Depending on which ethylene amine is added to the starting materials EDC and NH3, the reaction mixture comprises a corresponding proportion of higher ethylene amines. If, for example, TEPA is to be specifically produced, the ethylene amine TETA is added to the starting materials EDC and NH3. As a result, the product (ethylene amine mixture) comprises a higher proportion of TEPA, but also the abovementioned further linear and cyclic ethylene amines. Disadvantages of this process are, in particular, that the process proceeds with a low selectivity (gives an ethylene amine mixture) and that a specific ethylene amine (for example DETA) firstly has to be prepared and is subsequently introduced into the process to produce the next higher ethylene amine (for example TETA) in a targeted manner or to increase the yield. However, this process presents a corrosion problem because of the starting materials used (haloalkanes) and the hydrochloric acid formed and also an environmental problem because of the salts formed.
U.S. Pat. No. 3,462,493 relates to a process for preparing TETA, in which an at least five-fold molar excess of EDA is reacted with ethylene dichloride or ethylene dibromide. By-products formed here are, in particular, Pip or piperazinoethylethylenediamine.
DE-T 689 11 508 describes an alternative process for preparing linearly extended polyalkylene polyamines such as TETA. In this process, a bifunctional aliphatic alcohol is reacted with an amine reactant in the presence of a tungsten-comprising catalyst. A suitable bifunctional aliphatic alcohol is, in particular, monoethanolamine (MEA), and EDA or DETA can, for example, be used as amine reactants. This process gives principally mixtures of linearly extended polyalkylene polyamines (i.e. ethylene amine mixtures). These ethylene amine mixtures comprise the ethylene amines DETA, TETA, TEPA, Pip, AEPip or piperazine derivatives of higher ethylene amines, with the proportion of the respective components varying as a function of the amine reactants used. If DETA is used as amine reactant, an ethylene amine mixture having a high proportion of TETA and TEPA is obtained. Disadvantages of this process are that the process proceeds with a low selectivity (in respect of the components of the ethylene amine mixture obtained) and that an additional ethylene amine has to be synthesized first and then reacted with the bifunctional aliphatic alcohol (for example MEA). This forms relatively large amounts of by-products such as aminoethylethanolamine (AEEA) or higher hydroxy-comprising ethylene amines which are of little commercial interest. The relatively large amount of by-product formed is due to MEA or the higher ethanolamines (e.g. AEEA) being able to react with themselves instead of with the amine used. Owing to the (statistically) many possible reactions, the selectivity to the linear TETA is quite low because of the coproducts and cannot be controlled. The synthesis can be carried out only at a partial conversion.
An overview of the preparation of ethylene amines is given by the SRI report “CEH Product Review Ethyleneamines”, SRI International, 2003; pp. 1-53, in which EDA or DETA, in particular, are prepared by processes corresponding to those described above (using the starting materials EDC or MEA). Here, higher ethylene amines such as TETA or TEPA are formed as by-products or are obtained in higher yield by renewed reaction of the starting materials with EDA or DETA.
Thus, it is not disclosed anywhere in the prior art that mixtures of α-amino nitriles comprising, for example, AAN, IDAN, EDDN or other higher α-amino nitriles can also be hydrogenated. The processes according to the prior art are instead restricted to the hydrogenation of individual substances.